How Aircraft Engine Noise Can Be Measured

2023 Author: Hannah Pearcy | [email protected]. Last modified: 2023-06-05 00:21

Scientists at the German Aerospace Center (DLR) have used an unusual experimental setup to make the noise, which is generated by the engine jet on the wing flap of an aircraft, acoustically measurable.

The engine jet was simulated with a so-called engine simulator (TPS). The simulator weighs around 40 kg, has a diameter of 30 cm and an output of around 160 kW. In the test section of the Braunschweig low-speed wind tunnel (DNW-NWB), the DLR scientists tested such a simulator - complexly wired and wired, supplied with an oil pump, computer connection and heating.

During the tests, the simulator was in the simulated landing approach at 10,500 rpm, a jet speed of 460 km / h and a visible contrail. An aircraft wing was built directly behind the engine in the measurement section. A colorful signature on the source maps clearly showed: Not only is the engine loud, noise is also generated on the flap of the DLR wind tunnel model.

Simulated landing approach with realistic speed

While the simulator - a so-called "CRUF" engine (counter-rotating-ultra-high-bypass fan) - started with 21 bar of cold compressed air, the engine noise was distributed with about 60 decibels in the otherwise noiseless wind tunnel. Numerous microphones recorded the noise. The engine jet hit the extended wing flap at a realistic speed for the approach, which loomed centrally behind the CRUF in the test section. The display immediately rose by a few decibels - in the single-digit range, but this increase in noise is clearly audible to the naked ear. Even with an increase to 63 decibels, it seems to be twice as loud in the wind tunnel.

Filter sound sources and examine them separately

"We managed to measure the interaction of the engine and wing acoustically," explains Fabian Lange from the DLR Institute of Aerodynamics and Flow Technology. The fact that such a significant difference could be determined is a special result for the scientists, which will flow into further research into the jet valve interaction. "Now we can filter the sound sources from the 'total noise' of the engine and the trailing edge of the wing and examine them separately, " explains Fabian Lange.

This measurement result was made possible by the special experimental setup: With its large diameter and bypass ratio, the "CRUF" engine now enables scientists to predict for the first time how ever larger engines will have an aerodynamic and acoustic effect, how the large engines and wings will be configured more effectively and quietly in the future can be.

Measure entire aircraft in the wind tunnel

At the same time, the measurement results, which are the culmination and culmination of a long series of investigations in the context of the interdisciplinary DLR project KonTeKst (configurations and technologies for the low-emission and low-noise short-haul aircraft), flow into the development of new acoustic engine simulators. It is planned to develop an acoustic simulator in the follow-up project, which is no longer operated with compressed air, but with electricity. This will then be used to examine a complete half-model of an Airbus A320 in the wind tunnel. The aim and vision of the researchers is to be able to measure the aircraft as a whole in the wind tunnel acoustically and aerodynamically, rather than just individual components.